The present invention relates to an exposure apparatus using an electron beam or, in particular, to an improvement in an electrostatic deflector for an electron beam exposure apparatus using the electrostatic deflector as a subdeflector.
In recent years, integrated circuits have become more and more finely detailed with the density thereof ever on the increase. In place of the photolithography technology which has thus far been the main stream of the process of forming a fine pattern for many years, an exposure method using a charged particle beam such as an electron beam or an ion beam or a new exposure method using Xrays has been under study and has come to be realized. Among these developments, electron beam exposure for forming a pattern using an electron beam is in the spotlight as it can reduce the sectional area of the electron beam to several tens of nm and can form a pattern as fine as not more than 1 .mu.m. In step with this, the electron beam exposure apparatus is required to have stable operating characteristics, a high throughput and finer microfabrication characteristics.
In the conventional electron beam exposure apparatus, an electromagnetic deflector comparatively low in speed is used as a main deflector for an area (main deflection range) where the electron beam is deflected considerably on a specimen to be exposed (specifically, a wafer), while an electrostatic deflector comparatively high in speed is used as a subdeflector for each of several areas (subdeflection range) into which a main deflection range is segmented. The column of the electron beam exposure apparatus has built therein a projection lens for irradiating a wafer with an electron beam having an appropriately shaped section. The electromagnetic deflector and the electrostatic deflector described above are arranged substantially integrally with (i.e. in proximity to) the projection lens.
In the event that a metal having a superior machinability and a high accuracy but a high conductivity is used for the electrostatic deflector (subdeflector) or the peripheral parts thereof, an eddy current causes such inconveniences as a delayed response of the electromagnetic deflector (main deflector). This poses a critical problem for an electron beam exposure apparatus requiring a high throughput.
As a conventionally known technology, a cylindrical member of a nonconductor material (such as alumina) with the interior thereof plated (with NiP as a base and Au as a surface, for example) is used as the electrode of an electrostatic deflector. This technology has been a success to some degree. In this conventional technology, however, the electrode is shaped by extrusion molding, and therefore the problem is posed of the distortion of the electrode and the lack of uniformity of the plating of the cylindrical member interior. The result is that the quality is not necessarily constant and skill is required for assembling the electrode, thus making the technology unsuitable for mass production.
In the electron beam exposure apparatus, on the other hand, the interior of a column and the interior of an exposure chamber coupled to the column normally contain a high vacuum. Actually, however, the resist or the like used for exposure is evaporated, and when irradiated with an electron beam, burns and generates a chemical compound containing carbon or the like as a main component which is deposited on the surfaces in the apparatus. This deposit is not a good conductor, and therefore a charge is accumulated in the irradiated portion in a phenomenon called "charge-up". The resulting problem is that the electron beam is deflected to other than an originally intended place, thereby leading to a reduced exposure accuracy. Especially, this problem presents itself most conspicuously at an electrostatic deflector (subdeflector) located in the vicinity of the wafer coated with the resist.
In the prior art, the electrostatic deflector itself is replaced with a new one when the charge-up exceeds a certain amount. The replacing work, however, requires the provisional elimination (i.e. leakage from the atmosphere) of the high vacuum state in the column and the chamber. During the setup of the exposure apparatus (the initialization of the deflection data supplied to each deflector, for example) after the replacing job, the apparatus is stopped to reduce the throughput.
To cope with this problem, a method has been proposed, and used, in which the deposit is removed without atmosphere leaking into the interior of the column and the chamber (hereinafter referred to as "the in-situ cleaning method"). According to this method, a very slight amount of a gas containing oxygen as a main component is introduced into the apparatus, and in this thin gas environment, high frequency power is applied to the electrostatic deflection electrode. In this way, an oxygen plasma is generated so that the deposit is removed by ashing.
The in-situ cleaning method, though very effective, cannot necessarily be said to be fully satisfactory. As described above, the conventional electrostatic deflection electrode is shaped into a cylindrical form by extrusion molding and the interior thereof is plated. In an electrostatic deflection electrode of this configuration, however, not only the deposit containing carbon or the like as a main component attributable to the evaporation of the resist or the like but also an oxide is generated on the surface of the plated metal. The in-situ cleaning method, though effective for the deposit containing carbon or the like as a main component, is not effective for the oxide generated on the surface of the plated metal.
In view of this, the present inventor, after studying the materials and the properties of the materials of the electrode used for an electrostatic deflector, has test produced and conducted an experiment on an electrostatic deflector made of a material of the carbon group (graphite or vitreous carbon, for example) of which the oxide is evaporated. It has been found, however, that the material of the carbon group adversely affects the electron beam and is not usable due to the problem of the surface or the eddy current.
The inventor, after a further study of the materials and the properties of the materials of the electrode, has test produced (without plating) and conducted an experiment on a conductive ceramic AlTiC (a compound of alumina and titanium carbonate) having a substantially ideal resistivity (0.001 .OMEGA..cndot.cm to 1000 .OMEGA..cndot.cm). Although the problem of eddy current has not occurred, a slight charge-up was observed in the first round of the experiment. It has also been found that the use of the in-situ cleaning method increases the charge-up and the analysis shows that titanium oxide exists on the electrode surface thereby making the electrode unusable in this form.